1. Field of the Invention
The present invention relates to a nozzle touch apparatus for an injection molding machine.
2. Description of the Related Art
Conventionally, an injection molding machine comprises an injection apparatus and a mold apparatus. The injection apparatus is constructed such that resin heated and melted in a heating cylinder is injected from an injection nozzle. The injected resin is charged into a cavity of the mold apparatus. The molten resin is then cooled and solidified, and the mold apparatus is opened so as to permit removal of a molded article from the mold apparatus.
FIG. 1 is a conceptual diagram of a conventional injection molding machine, and FIG. 2 is a nozzle touch characteristic chart of the conventional injection molding machine. In FIG. 2, the horizontal axis represents an amount of deformation x, and the vertical axis represents a nozzle touch force f.
In FIG. 1, numeral 10 denotes an injection apparatus, numeral 11 denotes a heating cylinder, and numeral 13 denotes an injection nozzle provided at the front end (the left end in FIG. 1) of the heating cylinder 11. An unillustrated screw is disposed within the heating cylinder 11 such that the screw can be rotated and can be advanced and retracted by a drive section 12.
The screw extends rearwardly (rightward in FIG. 1) within the heating cylinder 11, and the rear end (the right end in FIG. 1) of the screw is connected to the drive section 12. The screw has a screw head at the front end thereof and a spiral flute formed on the peripheral surface of a metering portion of the screw, so that the flute defines a groove.
In the injection apparatus 10 having the above-described structure, during a metering stage, the drive section 12 is driven in order to retract the screw (rightward in FIG. 1), while rotating the screw in a forward direction. Consequently, pellet-shaped resin within an unillustrated hopper flows into the heating cylinder 11, and is caused to advance (move leftward in FIG. 1) along the groove of the screw. At this time, the resin is heated and melted by an unillustrated heater and accumulated on the front side of the screw head.
Further, during an injection stage, the drive section 12 is driven in order to advance the screw, so that the resin accumulated at the front side of the screw head is injected from the injection nozzle 13 and is charged into an unillustrated cavity of a mold apparatus 14. The mold apparatus 14 is composed of a stationary mold 15 and a movable mold 16. The movable mold 16 is advanced and retracted by an unillustrated mold clamping apparatus in order to bring the movable mold 16 into contact with the stationary mold 15 and separate the movable mold 16 from the stationary mold 15. Thus, mold closing, mold clamping, and mold opening are performed.
Subsequently, when the charging of resin into the cavity is completed, cooling water is caused to flow through an unillustrated cooling passage formed within the molding apparatus 14, so that the resin is cooled. After the resin is solidified, the molding apparatus is opened so as to permit removal of a molded product.
In the injection molding machine, resin may leak from a clearance between the injection nozzle 13 and the stationary mold 15 while the resin is being charge into the cavity, unless the injection nozzle 13 is in contact with the stationary mold 15 with a predetermined pressing force or nozzle touch force.
In order to solve the above-described drawback, a nozzle touch apparatus is provided. The nozzle touch apparatus advances the injection apparatus 10 such that the injection nozzle 13 comes in contact with the stationary mold 15 with a predetermined nozzle touch force. Thus, a nozzle touch operation is completed.
In order to perform the nozzle touch operation, a support member 22 and a motor 25 serving as drive means are fixed to a frame 21 of the injection molding machine; a ball screw shaft 23 is rotatably supported by the support member 22; and a ball nut 24 is in screw-engagement with the ball screw shaft 23. Further, the ball screw shaft 23 is connected to an output shaft 25a of the motor 25, and the ball nut 24 is connected to the injection apparatus 10 via a spring 26. A sensor 28 is disposed to face the spring 26. The sensor 28 senses a displacement of a certain portion of the spring 26 due to deformation of the spring 26 (hereinafter referred to as a xe2x80x9cdeforming positionxe2x80x9d) to thereby detect an amount of deformation.
In this case, when the ball screw shaft 23 is rotated through drive of the motor 25, the ball nut 24 is advanced from a retracted position, so that the injection apparatus 10 is advanced. Thus, the injection apparatus 10 reaches a nozzle touch position, and the injection nozzle 13 comes into contact with the stationary mold 15. Subsequently, when the motor 25 is further driven in a state in which the injection nozzle 13 is in contact with the stationary mold 15, the ball nut 24 is advanced against the urging force of the spring 26, so that the spring 26 contracts by an amount corresponding to the distance advanced by the ball nut 24. At this time, the injection nozzle 13 presses the stationary mold 15 with a force corresponding to the amount of deformation of the spring 26. When the deformation amount of the spring 26 is represented by x, and a pressing force that the injection nozzle 13 exerts on the stationary mold 15 or a nozzle touch force is represented by f, a relationship as shown in FIG. 2 exists between the deformation amount x and the nozzle touch force f. Accordingly, the nozzle touch force f can be detected through detection of the deforming position of the spring 26. When the deformation amount x reaches a preset value x1 and thus a proper nozzle touch force f equal to a target nozzle touch force f1 is generated, the motor 25 is stopped.
In the nozzle touch apparatus of the conventional injection molding machine, the injection apparatus 10 is connected to the ball nut 24 via the spring 26. Therefore, if an external force is applied to the injection apparatus 10 due to impact caused by, for example, closing or opening of the molding apparatus 14 or injection of resin, the spring 26 is expanded or contracted, so that the deformation amount x varies.
Therefore, even when the ball nut 24 is accurately positioned, the sensor 28 may erroneously detect the deformation amount x due to expansion or contraction of the spring 26 caused by an external force. In this case, the nozzle touch force f is not accurately detected, with the result that a proper nozzle touch force f equal to the target nozzle touch force f1 cannot be generated. For example, when the spring 26 is contracted, the nozzle touch force f becomes excessively large, resulting in breakage of the mold apparatus 14 and/or nozzle 13. When the spring 26 is expanded, the nozzle touch force f becomes excessively small, resulting in resin leaking from the clearance between the injection nozzle 13 and the stationary mold 15.
Since the spring 26 and the sensor 28 are attached to the injection apparatus 10, the spring 26 and the sensor 28 are accommodated within an unillustrated casing of the injection apparatus 10, which deteriorates ease of maintenance and management of the injection molding machine.
An object of the present invention is to solve the above-mentioned problems in the conventional nozzle touch apparatus for an injection molding machine, to provide a nozzle touch apparatus for an injection molding machine which can accurately detect nozzle touch force, which can generate a proper nozzle touch force, and/or which facilitates work for maintenance and management of the injection molding machine.
A nozzle touch apparatus for an injection molding machine according to one example of the present invention comprises: a frame; an injection apparatus having an injection nozzle, said injection apparatus being disposed to be movable relative to said frame, moving means for moving said injection nozzle of said injection apparatus towards and away from a mold, said injection nozzle thus being movable to abut said mold with a nozzle touch force, and first energy absorption means disposed between said moving means and said frame for absorbing mechanical energy relating to the nozzle touch force.
Other aspects of the invention and their advantages will become apparent with reference to the following description of one detailed example of the invention.